Swellable downhole structures including carbon nitride materials, and methods of forming and using such structures

ABSTRACT

A swellable downhole article includes a swellable material and a carbon nitride material. The swellable material may include at least one of an elastomeric material and an absorbent material. The carbon nitride material may remove cations from a downhole fluid. Methods of forming the swellable downhole article are also disclosed, as are methods of forming a carbon nitride containing material for removing contaminants from a fluid.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.14/140,053, filed Dec. 24, 2013, pending, the disclosure of which ishereby incorporated herein in its entirety by this reference.

TECHNICAL FIELD

Embodiments of the disclosure relate generally to materials for removingcontaminants from a fluid and methods of forming such materials. Moreparticularly, embodiments of the disclosure relate to downholestructures including a carbon nitride material for removing contaminantsfrom a fluid and methods of forming downhole articles including carbonnitride materials and a swellable material.

BACKGROUND

The drilling of wells for oil and gas production conventionally employslongitudinally extending sections or so-called “strings” of drill pipeto which, at one end, is secured a drill bit of a larger diameter. Aftera selected portion of the borehole has been drilled, the borehole isusually lined or cased with a string or section of casing or liner. Sucha casing or liner exhibits a larger diameter than the drill pipe used todrill the borehole, and a smaller diameter than the drill bit.Conventionally, after the casing or liner string is placed in theborehole, the string is cemented into place.

Tubular strings, such as drill pipe, casing, or liner, may be surroundedby an annular space between the exterior wall of the pipe and theinterior wall of the well casing or the borehole wall, for example.Frequently, it is desired to seal such an annular space between upperand lower portions of the well depth. The annular region may be sealedwith a downhole article that seals the annular space, such as between acasing wall and a tubular component, such as a length of productiontubing. Swellable packers are particularly useful for sealing an annularspace because they swell (e.g., expand) upon exposure to wellbore fluidsand fill the cross-sectional area of the annular space in response tocontact with one or more downhole fluids. Such materials that swell uponexposure to a fluid without negatively affecting the properties of thematerial are referred to herein as “swellable materials.”

However, contaminants such as metallic cations within the wellbore fluidmay negatively affect the operation of swellable materials. For example,cations within the wellbore fluid may increase the amount of time ittakes for a swellable material to fully expand, may decrease the totalamount of swelling of the swellable material, and may acceleratedegradation of the swellable material.

In the subterranean hydrocarbon (i.e., oil and gas), as well asgeothermal drilling and completion industries, fluids containingcontaminants (referred to in the industry as flowback fluids) often mayreturn to the surface. Because the flowback fluids contain contaminants,environmental regulations often require that the flowback fluids betreated before they are discharged or reused.

It would, therefore, be desirable to have improved methods of removingcontaminants from both wellbore fluids and flowback fluids. It wouldalso be desirable to have improved methods of forming a swellabledownhole article for sealing an annular space within the interior of awellbore in the presence of cations.

BRIEF SUMMARY

In some embodiments, the disclosure includes a swellable downholearticle that includes a swellable material having an inner diameterconfigured for receiving an outer diameter of a portion of a tubularcomponent for disposition in a borehole. The swellable materialcomprises at least one of an elastomeric material and an absorbentmaterial. The swellable downhole article includes a carbon nitridematerial configured for removing cations from a wellbore fluid.

In additional embodiments, a method of forming a swellable downholearticle is disclosed. The method includes forming a swellable materialcomprising at least one of an elastomeric material and an absorbentmaterial, the swellable material formulated and configured to expandfrom an initial state to a swollen state upon contacting a wellborefluid. A carbon nitride material is provided within the swellabledownhole article.

In additional embodiments, a method of forming a material for removingcontaminants from a fluid comprises forming a carbon nitride material tohave a structure comprising vacancies between triazine rings of thecarbon nitride material. The carbon nitride material is admixed with atleast one of an elastomeric material, polyurethane, polyurea, polyamine,carbon black, graphite, carbon fiber, glass fiber, silica, clays,calcium carbonate, bentonite, polytetrafluoroethylene, and molybdenumdisulfide. At least one of a filter and a membrane is formed from thecarbon nitride material. The at least one of a filter and a membranecomprises from between about fifteen percent by weight to aboutthirty-five percent by weight of the carbon nitride material.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming what are regarded as embodiments of theinvention, the advantages of embodiments of the disclosure may be morereadily ascertained from the following description of certainembodiments of the disclosure when read in conjunction with theaccompanying drawings, in which:

FIG. 1A is a cross-sectional side view of a swellable downhole articleincluding a swellable material that may include carbon nitride;

FIG. 1B is a cross-sectional side view of the swellable downhole articleof FIG. 1A showing the swellable material in an expanded state;

FIG. 2 is a cross-sectional side view of a swellable downhole articleincluding a swellable material surrounded by a shell that may includecarbon nitride;

FIG. 3 is a cross-sectional side view of a swellable downhole articleincluding a swellable material and a filter material that may includecarbon nitride;

FIG. 4A is a cross-sectional side view of a swellable downhole articleincluding a swellable material and a membrane material that may includecarbon nitride;

FIG. 4B is a cross-sectional side view of the downhole article of FIG.4A showing the swellable material in an expanded state;

FIG. 5 is a cross-sectional side view of a system including a carbonnitride material; and

FIG. 6 schematically illustrates a system for removing contaminants froma fluid using a carbon nitride material.

DETAILED DESCRIPTION

Illustrations presented herein are not meant to be actual views of anyparticular material, component, or system, but are merely idealizedrepresentations that are employed to describe embodiments of thedisclosure. Elements common between figures may retain the samenumerical designation.

The following description provides specific details, such as materialtypes, compositions, material thicknesses, and processing conditions inorder to provide a thorough description of embodiments of thedisclosure. However, a person of ordinary skill in the art willunderstand that the embodiments of the disclosure may be practicedwithout employing these specific details. Indeed, the embodiments of thedisclosure may be practiced in conjunction with conventional techniquesemployed in the industry. Only those process acts and structuresnecessary to understand the embodiments of the disclosure are describedin detail below. Additional acts to form a complete swellable downholearticle or a material to remove contaminants may be performed byconventional techniques.

A carbon nitride material may bind contaminants from process fluids suchas wellbore fluids and flowback fluids. In some embodiments, the carbonnitride material binds cations within a wellbore fluid, to mitigate thenegative effects of such cations on swellable materials. The carbonnitride material may be integrated into a swellable downhole article tobind cations within wellbore fluids and protect the swellable materialfrom being damaged by the cations in the wellbore fluid. In otherembodiments, the carbon nitride material may be used to purify fluidsprior to discharging the flowback fluids to underground injection wellsor back to surface water systems.

An embodiment of a swellable downhole article 100 including a swellablematerial 140 is shown in FIG. 1A. The swellable material 140 maysurround a section of a tubular component 120 within a wellbore. Thetubular component 120 may be a portion of a downhole casing or linerstring, production pipe or tubing, or other tubular component within thewellbore. The swellable material 140 may be activated to swell based onthe properties of the components of the swellable material 140. Becausethe swellable material 140 expands after exposure to wellbore fluids, inan initial state, the swellable material 140 may be placed on tubularcomponent 120 in an initial un-swollen configuration in which theswellable material 140 has a smaller diameter than the diameter of wall105 of borehole 160 (FIG. 1B).

Referring to FIG. 1B, the swellable material 140 is shown in the swollen(e.g., expanded) state. Exposure to a wellbore fluid causes theswellable material 140 to expand and engage the wall 105 of borehole160, thereby forming a compression seal between the tubular component120 and the wall 105. Thus, the outer diameter of the swellable material140 may increase until it contacts the wall 105 of borehole 160 withinsubterranean formation 115. In other embodiments, an inner wall oftubing, casing, liner, or other surface may be a downhole structureengaged by the swellable material 140 surrounding tubular component 120.Thus, an annulus between an outer downhole structure such as asubterranean formation 115 or larger, outer tubular component (e.g.,borehole 160) and a smaller, inner tubular component 120 may be isolatedby expansion of the swellable material 140 such that fluids (e.g., fromformation 115) are substantially prevented from flowing past theswellable material 140 once the swellable material 140 is expanded. Asindicated above, the swellable material 140 may be used in either openborehole structures or cased or lined borehole structures.

The swellable material 140 may include one or both of an elastomericmaterial and an absorbent material. The elastomeric material maycomprise any swellable or non-swellable material. In some embodiments,the elastomeric material is absorbent with respect to one or moredownhole fluids.

The elastomeric material may include a rubber material such as naturalrubber or a synthetic rubber copolymer. In some embodiments, theelastomeric material may include acrylonitrile butadiene styrene (ABS),polyacrylonitrile (PAN), a nitrile-based elastomer, such asacrylonitrile butadiene rubber (NBR, also known as Buna-N or Purbunan),and combinations thereof. The elastomer may comprise various grades ofNBR such as hydrogenated acrylonitrile butadiene rubber (HNBR),carboxylated acrylonitrile butadiene rubber (XNBR), carboxylatedhydrogenated acrylonitrile butadiene rubber (XHNBR), and combinationsthereof. The elastomeric material may also comprise fluorinated polymerrubbers, tetrafluoroethylene propylene rubbers, fluorosilicone rubber,butyl rubbers, and combinations thereof.

The elastomeric material may be crosslinked. The crosslinks may includesulfur, peroxide, urethane, metallic oxides, boron oxide, acetoxysilane,alkoxysilanes and combinations thereof. In some embodiments, thecrosslink is a sulfur or a peroxide crosslink.

The swellable material 140 may include one or more absorbent materialsthat are compatible with the elastomeric material. The absorbentmaterial may increase the swellability of the swellable material 140. Insome embodiments, an acrylate polymer or acrylate copolymer (AC) may beadded to the elastomeric material. The AC may comprise a mixturecomprising from between about twenty-five percent by weight (25 wt. %)to about seventy-five percent by weight (75 wt. %) of an active polymerand from between twenty-five percent by weight (25 wt. %) to aboutseventy-five percent by weight (75 wt. %) of a phthalate ester. In oneembodiment, the AC comprises about fifty percent by weight (50 wt. %)active polymer and fifty percent by weight (50 wt. %) of a phthalateester. Non-limiting examples of the active polymer include copolymers ofacrylic acid and its esters, polyacrylamide copolymer, ethylene maleicanhydride copolymers, polyvinyl alcohol copolymers, crosslinkedpolyethylene oxide, a copolymer of polyacrylonitrile (PAN), an ethylenepropylene diene monomer (EPDM), methyl acrylate, ethyl acrylate, butylacrylate, acrylic acid alkylester, and combinations thereof.

The absorbent material may also include a cellulose material. In someembodiments, the cellulose material is carboxy methyl cellulose (CMC).The CMC may comprise a dry powder and the AC may be a liquid mixture.Adding an AC and the CMC material to the elastomeric material mayincrease the total swellability of the swellable material 140 more thanadding each of the AC and the CMC individually to the swellable material140. In some embodiments, the swellable material 140 may comprise fromabout fifteen percent by weight (15 wt. %) to about thirty-five percentby weight (35 wt. %) of each of the elastomeric material, the AC, andthe CMC.

The swellable material 140 may further comprise other additivesincluding filler materials, activators, antioxidants, process aids,curatives, and accelerators. Suitable filler materials include carbonblack, carbon fiber, glass fiber, silica, clays, calcium carbonate,bentonite, polytetrafluoroethylene (PTFE), molybdenum disulfide (MoS₂),graphite, and combinations thereof. The filler material may range frombetween about 30 parts per hundred rubber (phr) to about 100 phr. Theactivator may include magnesium oxide, zinc oxide, zinc stearate,stearic acid, and combinations thereof and may range from between about1 phr to about 10 phr. The antioxidant may include a diphenyl amine, amercaptobenzimidazole, and combinations thereof. The process aids mayinclude a wax, an oligomer, a resin, a fluorocarbon, stearic acid, lowmolecular weight polyethylene, and combinations thereof. Theantioxidants and the process aids may range from between about 0.5 phrto about 5.0 phr. Curatives may include sulfur, peroxide, acrylateesters, methacrylate esters, dimaleimides, allyl-containing cyanurates,isocyanurates (e.g., triallyl isocyanurate (TAIC)), phthalates, andcombinations thereof. The accelerators may include mercapto compoundssuch as 2-mercaptobenzothiazole (MBT) and mercaptobenzothiazyl disulfide(MBTS), sulfonamides such as benzothiazyl-2-t-butyl sulfonamide (TBBS),and thiurams such as tetramethyl thiuram disulfide (TMTD). The curativesand accelerators may range from between about 0.2 phr to about 3.0 phr.

The swellable material 140 may be formed by mixing the elastomericmaterial with the absorbent material to form a composition. In someembodiments, other additives such as fillers, activators, antioxidants,process aids, curatives, and accelerators may be added to thecomposition. The components of the swellable material 140 may be blendedor compounded by conventional methods. For example, the absorbentmaterial including AC and CMC may be emulsified in a nitrile soluble oiland mixed with the elastomeric material. The oil may include aparaffinic-based oil, a naphthenic-based oil, an aromatic-based oil, aphthalate ester, and combinations thereof. The composition may be mixedin a mill mixer, a banbury mixer, or other mixer. The resulting materialmay be cured and formed into a desired shape, such as by extruding orpressing. In some embodiments, the composition may be formed as a ringwith an internal diameter sized and configured for receiving a tubularcomponent (e.g., tubular component 120) therethrough.

The composition described above may form the swellable material 140 andmay swell upon exposure to a wellbore fluid. However, wellbore fluidsoften contain heavy metals and other contaminants that may increase thetime for the swellable material 140 to swell or decrease the totalamount of swelling of the swellable material 140.

For example, wellbore fluids may include an aqueous component such as abrine solution containing various ions formed from dissolved salts. Thecations may include cations of cations of barium (Ba²⁺), cations ofchromium (Cr²⁺, Cr³⁺), cations of copper (Cu⁺, Cu²⁺), cations of iron(Fe²⁺, Fe³⁺), cations of potassium (K⁺), cations of magnesium (Mg²⁺),cations of manganese (Mn²⁺), cations of molybdenum (Mo²⁺), cations ofsodium (Na⁺), cations of nickel (Ni²⁺), cations of lead (Pb²⁺, Pb⁴⁺),cations of titanium (Ti³⁺), cations of zinc (Zn²⁺), sulfate ions (SO₄²⁻), other metal ions, and combinations thereof. To mitigate thenegative effects of cations in the wellbore fluid on the swellablematerial 140, a carbon nitride material may bind the cations dispersedwithin the wellbore fluid.

In general, higher concentrations of cations in the wellbore fluid mayslow the rate of swelling and lower the total amount of swelling of theswellable material 140. In addition to reducing the amount of swellingof the swellable material 140, cations such as Zn²⁺ in the wellborefluid may damage and degrade the swellable material 140 and mayeventually break the seal between the swellable material 140 and theborehole 160, between the swellable material 140 and the tubularcomponent 120, or both.

The concentration of cations in the wellbore fluid contacting theswellable material 140 may be reduced by incorporating a carbon nitridematerial into the swellable downhole article 100. The carbon nitridematerial may bind cations within the wellbore fluid, thereby mitigatingthe negative effects of the cations on the swellable material 140. Thecarbon nitride material may be formed as an integral part of swellablematerial 140, may be formed as a filter or membrane through which thewellbore fluid travels prior to contacting the swellable material 140,and combinations thereof.

One advantage of using a carbon nitride material to bind cations withina fluid is the ability of the carbon nitride material to withstand highpressure and high temperature environments, such as those encountereddownhole. For example, carbon nitride may withstand temperatures up toapproximately 400° C., such as between about 350° C. and about 400° C.Other materials that may remove contaminants from a wellbore fluid, suchas functionalized graphenes, may be sensitive to higher temperatures.For example, such materials may lose functionality at temperatures ofapproximately 180° C. and higher.

The carbon nitride material may comprise a C₃N₄ polymer material. TheC₃N₄ may be an amorphous carbon nitride or a graphitic carbon nitride.In one embodiment, the C₃N₄ structure is a graphitic carbon nitridehaving a spherical shape. Generally, the carbon nitride material mayhave a chemical structure as shown below, where nitrogen atoms formbridges between adjacent triazine structures.

The carbon nitride of the C₃N₄ carbon nitride structure may includes-triazine rings (i.e., 1,3,5-triazine) bridged together by nitrogenatoms between adjacent triazine rings. The geometry of the C₃N₄ carbonnitride structure may not be planar but may be substantially spherical,similar to buckminsterfullerene structures. The carbon nitride may beformed as spherical structures with diameters ranging from between about30 nm to about 2,000 nm. In some embodiments, the carbon nitride mayhave an average particle diameter of between about 100 nm and about1,000 nm. The C₃N₄ structure may result in a multi-walled structure.Adjacent walls of the multi-walled structure may be separated by betweenabout 3 Å and about 4 Å. In some embodiments, the distance betweenadjacent walls of the multi-walled structures may be about 3.415 Å.

The graphitic carbon nitride structure may inherently include vacancies(e.g., voids) that may act as sites for binding contaminants dispersedwithin a fluid. For example, the carbon nitride may bind metal cationsin the vacancies that are inherently formed in the middle of triangularshaped openings formed by nitrogen atoms bridging adjacent trizainerings. Thus, the carbon nitride may effectively remove contaminantswithout the need to functionalize the carbon nitride. In someembodiments, cations bound within an outer layer of a multi-walledcarbon nitride structure may be moved from an outer wall to an innerwall of the carbon nitride structure.

The carbon nitride may be formed through a variety of chemicalreactions. For example, the carbon nitride may be formed by thepolymerization of cyanamide (CH₂N₂), dicyanamide (C₂H₄N₄), or melamine(C₃H₆N₆) or by the pyrolysis of melamine. In some embodiments, thecarbon nitride is formed by chemical vapor deposition (CVD) with acarbon containing precursor and a nitrogen containing precursor. Thecarbon containing precursor may include methane, ethane, s-triazinerings, and combinations thereof. The nitrogen containing precursor mayinclude ammonia, nitrogen gas, s-triazine rings, and combinationsthereof. In other embodiments, the carbon nitride is formed by reactinglithium nitride (Li₃N) with cyanuric chloride (C₃N₃Cl₃) or cyanuricfluoride (C₃N₃F₃) to form C₃N₄ and a lithium chloride salt or lithiumfluoride salt.

The carbon nitride may be more effective at removing cations at aneutral pH than at a low pH. The carbon nitride may capture cations froma fluid at a pH ranging from between about 6.0 to about 8.0. In someembodiments, the carbon nitride may capture contaminants from a fluidhaving a pH of about 7.0. Since the carbon nitride captures more ions ata neutral pH, exposing the carbon nitride to a lower pH may releasecations bound within the carbon nitride structure. Thus, as thevacancies of the carbon nitride become saturated with bound cations, thecarbon nitride may be regenerated to free vacancies within thestructure. In some embodiments, the carbon nitride is regenerated byexposing the carbon nitride to a low pH, thereby freeing bound cationswithin the carbon nitride. Then, the fluid surrounding the carbonnitride may be purged from around the carbon nitride and the carbonnitride may continue to capture cations within a fluid.

To further increase the ability of the carbon nitride to capture andbind the contaminants of a fluid, the carbon nitride may befunctionalized. For example, the graphitic carbon nitride structure mayinclude terminal amino groups and hydroxyl groups at ends of thestructure. These terminal amino and hydroxyl groups may befunctionalized to alter the chemical or physical properties of thecarbon nitride. In some embodiments, the terminal groups may be replacedwith a hydrophilic or a hydrophobic group to make the carbon nitridehydrophobic or hydrophilic. In other embodiments, the terminal groupsmay be functionalized with other materials that may increase thecompatibility of the carbon nitride material with the elastomericmaterial of the swellable material 140. For example, the carbon nitridemay be functionalized with alkyl groups, vinyl groups, epoxide groups,silane groups, carboxyl groups, pyridine groups, phenolic groups, andcombinations thereof.

In some embodiments, a swellable material 140 may include a carbonnitride material. The swellable material 140 may be comprised of ahomogeneous composition with the elastomeric material and the absorbentmaterial. In some embodiments, carbon nitride may be mixed with theelastomeric material, the absorbent material, and any other additives toform a composition. The carbon nitride may be compatible with thecomposition of the swellable material 140. For example, in someembodiments, carbon nitride may be added to the composition of theswellable material 140. The carbon nitride may replace at least aportion of a filler material in the swellable material 140. Thus, insome embodiments, the swellable material 140 may also be free of carbonblack filler material. The elastomeric material, the absorbent material,the carbon nitride, and any other additives may be emulsified in anitrile soluble oil. The composition may be dried, extruded, and pressedinto a desired shape or form. Thus, the carbon nitride material may behomogeneously incorporated into the swellable material 140. Theswellable material 140 may comprise from between about fifteen percentby weight (15 wt. %) to about thirty-five percent by weight (35 wt. %)carbon nitride.

In other embodiments, the swellable material 140 may be formed bycombining the elastomeric material, the absorbent material, and at leastone additive to form a composition. The composition may be extruded andshaped into a desired shape to form the swellable material 140. Then,the swellable material 140 may be coated with carbon nitride toencapsulate the swellable material 140 with carbon nitride. For example,the carbon nitride may be mixed with an oil and then coated onto theswellable material 140 and allowed to dry.

Referring to FIG. 2, a cross-sectional view of a swellable downholearticle 200 bearing a tubular component 220 is shown. A swellablematerial 240 may surround an outer diameter of the tubular component220. The swellable downhole article 200 may also include a shell 230comprising a carbon nitride material at least partially surrounding theswellable material 240. The carbon nitride material of the shell 230 maybe bound together by reacting terminal amino groups of the carbonnitride with polyurethane, polyurea, a polyamine, or combinationsthereof. The swellable material 240 may also comprise a carbon nitridematerial as described above.

The swellable downhole article 200 may be configured such that anywellbore fluid passes through the shell 230 prior to contacting theswellable material 240. Because the shell 230 may be comprised of acarbon nitride material, cations in the wellbore fluid may be removedprior to the wellbore fluid contacting the swellable material 240.

In some embodiments, a coating 250 may be formed on the outer surface ofthe shell 230. The coating 250 may comprise an elastomer that issubstantially impermeable to the wellbore fluid and may protect theswellable material 240 and carbon nitride material of the shell 230 frompremature contact with wellbore fluid during run-in procedures.

An valve or other openable orifice 260 may penetrate the coating 250 tocontrol fluid communication to the carbon nitride material of the shell230 and to the swellable material 240. The openable orifice 260 may be aneedle valve plugged with a degradable material, a water-solublepolymer, or a controlled electrolytic material (CEM) such as magnesiumor alloys thereof. The CEM may be controllably dissolved by contactingwellbore fluids or may be removed by an electrochemical reaction. Afterthe CEM coating is removed from the openable orifice 260, wellbore fluidflows through the openable orifice 260, and the carbon nitride of theshell 230 binds cations located in the wellbore fluid.

Referring to FIG. 3, in another embodiment, a swellable downhole article300 may include a tubular component 320. A swellable material 340 maysurround an outer diameter of the tubular component 320. The swellabledownhole article 300 may include a filter 370 comprised of carbonnitride. The carbon nitride may be in the form of sheets, nanosheets,spheres, flakes, pellets, powder, or other suitable form. The carbonnitride of the filter 370 may be bound together by reacting terminalamino groups of carbon nitride with polyurethane, polyurea, a polyamine,or combinations thereof during their curing. The filter 370 may removeor filter ions from the wellbore fluid before the wellbore fluidcontacts the swellable material 340.

The swellable downhole article 300 may include a valve or openableorifice 360 similar to valve or openable orifice 260 described abovewith reference to FIG. 2. The openable orifice 360 may control the flowof fluid through the filter 370 and to the swellable material 340. Theopenable orifice 360, when open, may create a passageway forcommunicating fluid to the filter 370 and through the filter 370 to theswellable material 340. Thus, the flow of wellbore fluid may be filteredof ions by the filter 370 before reaching the swellable material 340.The swellable material 340 may expand to contact wall 305 after beingcontacted by the filtered wellbore fluid.

Referring to FIG. 4A, a swellable downhole article 400 is shownincluding a membrane 480 comprising carbon nitride surrounding a tubularcomponent 420. The membrane 480 may comprise a permeable material suchas a porous foam or fiber in which the carbon nitride material isdispersed. The membrane 480 may overlie a swellable material 440. Acoating 450 comprising an elastomeric material may overlie and at leastpartially surround the swellable material 440 and the membrane 480. Avalve or other openable orifice 460 may extend through the coatingmaterial 450 to control fluid communication to the membrane 480 and theswellable material 440.

Referring to FIG. 4B, the swellable downhole article 400 is shown afterthe swellable material 440 has expanded to a swollen state. As shown,the expanded swellable material 440 may force the coating material 450to seal against a wall 405 of a wellbore casing, liner, tubing, otherdownhole element, or subterranean formation.

In some embodiments, additional elements may be added to the swellablematerial to further remove contaminants and cations from the wellborefluid as disclosed in, for example, one or more of U.S. patentapplication Ser. No. 13/646,028, filed Oct. 5, 2012, published as U.S.Patent Application Publication No. 2013/0126185, now U.S. Pat. No.9,284,812, issued Mar. 3, 2016, and entitled SYSTEM FOR INCREASINGSWELLING EFFICIENCY; and U.S. patent application Ser. No. 13/300,916,filed Nov. 21, 2011, published as U.S. Patent Application PublicationNo. 2013/0126190, and entitled ION EXCHANGE METHOD OF SWELLABLE PACKERDEPLOYMENT, the disclosures of which applications are incorporatedherein in their entireties by this reference.

In some embodiments, at least one of an ion exchange material and afunctionalized graphene may be added to the swellable material describedwith reference to any of FIG. 1A through FIG. 4B. The ion exchangematerial or the functionalized graphene may comprise discrete particleswithin the swellable material. Thus, the swellable material may includea homogeneous composition including an elastomeric material, anabsorbent material, an ion exchange material, a functionalized graphene,additives, and combinations thereof. In other embodiments, the ionexchange material or the functionalized graphene may be formed as partof a shell 230 (FIG. 2), disposed within a filter 370 (FIG. 3), or aspart of a membrane 480 (FIG. 4A) through which wellbore fluid passesprior to contacting swellable material 140, 240, 340, 440. In theseembodiments, the swellable material 140, 240, 340, 440 may also includea carbon nitride material in addition to the shell 230 (FIG. 2), filter370 (FIG. 3), or the membrane 480 (FIG. 4A). The ion exchange materialand the functionalized graphene may remove additional cations that maynot be removed by the carbon nitride.

The ion exchange material may be an ion exchange membrane, ion exchangeresin, inorganic mineral (e.g., a zeolite, silica, alumina, titania),and combinations thereof. The ion exchange material may comprise anorganic polymer that may include functional groups having chargedgroups. By way of non-limiting example, the functional groups may beeither anionic, cationic, or combinations thereof. Non-limiting examplesof anionic functional groups include sulfonic acid groups (e.g.,polystyrene sulfonic acid), phosphonic acid groups, polyacrylic acid,polymaleic acid, poly(vinyl toluene sulfonic acid), poly(styrenesulfonate-co-maleic acid), poly(vinyltoluene sulfonate-co-maleic acid),poly styrene carboxylate, poly(alkylvinyl ether-co-maleic acid),sulfonated polyvinyl alcohol,poly(acrylamide-co-2-acrylamido-2-methylpropane carboxylate),poly(acrylamide-co-2-acrylamido-2-methylpropane sulfonate), poly(styrenesulfonate-co-acrylamide), poly acrylic acid, poly(styrenecarboxylate-co-acrylamide), poly(2-acrylamide-2-methylpropanesulfonate-co-maleic acid), poly(styrene sulfonic acid),poly(2-acrylamido-2-methyl-1-propanesulfonic acid), salts thereof, andcombinations thereof. Where the functional group includes a cationicfunctional group, the functional group may include a primary aminogroup, a secondary amino group, a tertiary amino group, a quaternaryphosphonium group, a tertiary sulfonium group, alkyl pyridinium group,and combinations thereof.

The charged functional group of the organic polymer may be associatedwith a counter ion. The counter ion may dissociate from the chargedfunctional group and be replaced with an ion from the wellbore fluid.The counter ion may include a hydroxide, a halide, a sulfate, a nitrate,hydrogen, or an alkali metal such as lithium, sodium, or potassium.

The ion exchange material may be selected to affect the pH of thedownhole environment. For example, a polymer comprising protonatedcations or a zeolite may decrease the pH of a wellbore fluid while ahydroxide counter ion may increase the pH of the wellbore fluid. Thus,in some embodiments, an ion exchange material may be selected to controlthe pH of the wellbore fluid and optimize the functionality of thecarbon nitride. For example, the ion exchange material may control thepH of the wellbore fluid surrounding the swellable material to a rangebetween about 6.0 and about 8.0. In one embodiment, the pH of thewellbore fluid surrounding the swellable material is about to about 7.0.

The functionalized graphene material may include a graphene, grapheneoxide, graphite, graphite oxide, and combinations thereof. Thefunctionalized graphene materials may be functionalized with thiolgroups, carboxylic acid groups, carbonyl groups, disulfide groups,sulfonic acid groups, iminodiacetic acid groups,N-[5-amino-1-carboxy-(t-butyl)pentyl]iminodi-t-butylacetate groups,N-(5-amino-1-carboxypentyl)iminodiacetic acid groups, aminocaproicnitrilotriacetic acid groups, aminocaproic nitrilotriacetic acidtri-tert-butylester groups, 2-aminooxyethyliminodiacetic acid groups,quaternary ammonium groups, quaternary phosphonium groups, ternarysulfonium groups, cyclopropenylium groups, primary amino groups,secondary amino groups, tertiary amino groups, and combinations thereof.

In additional embodiments, the present disclosure includes a method ofsealing an annular portion of a wellbore. The method includes forming aswellable material comprising a carbon nitride material in an annulusbetween a downhole article and a wall of a wellbore, binding ions of awellbore fluid with the carbon nitride material, and contacting theswellable material with the wellbore fluid.

In other embodiments, a downhole article including a swellable materialand a carbon nitride material is formed. The method includes forming aswellable material comprising at least one of an elastomeric materialand an absorbent material. The swellable material may be configured toexpand from an initial state to an expanded state upon contacting awellbore fluid. The method includes forming a carbon nitride materialwithin the swellable downhole article.

In other embodiments, a carbon nitride material may capture cations andother contaminants from fluids such as flowback fluids. The flowbackfluids often contain contaminants such as uranium, arsenic, radon,mercury, radium, thorium, lead, nickel, and other heavy metals. Prior toreusing or discharging the flowback fluids, the fluids must be treatedto remove the contaminants.

Contaminants from the flowback fluids may be removed by treating themwith a carbon nitride material. The fluids may be treated in pits ortanks, may be treated in industrial wastewater treatment facilities, ormay be treated in situ.

Referring to FIG. 5, a flowback fluid may be treated in situ in a system500. The system 500 may include element 560 comprising carbon nitride.Element 560 may comprise a filter, a membrane, and combinations thereof.The system 500 may be part of a wellbore or may be located in piping 505aboveground. The element 560 may be disposed within a tubular component520 such that any fluid travelling through the tubular component 520passes through the carbon nitride of the element 560. The carbon nitridedisposed within the element 560 may be in powder, pellet, spherical, orother form. The carbon nitride may be as described above. For example,the carbon nitride may be functionalized, may be reacted and boundtogether by reacting the carbon nitride with a polyurethane, polyurea, apolyamine, and combinations thereof. Although shown in only one sectionof tubular component 520, the element 560 may be located in a pluralityof locations within system 500.

In other embodiments, a material comprising carbon nitride may beformed. The material may be useful for removing contaminants from afluid. The method includes forming a carbon nitride material. The carbonnitride material may have a structure including vacancies that may bebinding sites for capturing contaminants located within the fluid. Thecarbon nitride may be admixed or reacted with NBR, HNBR, XNBR, XHNBR,ABS, PAN, polyurethane, polyurea, a polyamine, and combinations thereofto bind the carbon nitride material together. Other additives may beadded to the carbon nitride material, such as carbon black, carbonfiber, glass fiber, silica, clays, calcium carbonate, bentonite,polytetrafluoroethylene (PTFE), molybdenum disulfide (MoS₂), andgraphite. A binder may be added to the composition. Non-limitingexamples of the binder include an acrylic resin binder, an acrylicpolymer, and combinations thereof. The composition may be agglomeratedand pressed into a desired shape, such as sheets, nanosheets, spheres,flakes, pellets, and powder. The composition including the carbonnitride may be added to a housing configured for receiving fluid flow.

In some embodiments, the carbon nitride material may comprise a portionof a filter. In other embodiments, the carbon nitride may comprise amembrane material comprising a permeable material such as a porous foamor fiber with the carbon nitride material disposed on or within thepermeable material. The filter or the membrane may comprise betweenabout five percent by weight (5 wt. %) to about one hundred percent byweight (100 wt. %) carbon nitride. In some embodiments, the carbonnitride may comprise between about five percent by weight (5 wt. %)about fifteen percent by weight (15 wt. %), between about fifteenpercent by weight (15 wt. %) and about thirty-five percent by weight (35wt. %), or between about thirty-five percent by weight (35 wt. %) andabout fifty percent by weight (50 wt. %) based on the total weight ofthe filter or membrane. The carbon nitride material may be used to treatindustrial wastewater. For example, as described above with reference toFIG. 5, water to be treated may be passed through a filter or membranecomprising the carbon nitride material to remove contaminants from thewater.

Referring to FIG. 6, a system 600 including an aboveground water storagepit or tank 610 is shown. The tank 610 may be at least partially filledwith a flowback fluid 620 containing contaminants. The tank 610 mayinclude one or more mixers 630 for mixing the flowback fluid 620. Avalve 640 may be located at the inlet of the tank 620 and a valve 645may be located at the outlet of the tank 610. The outlet of the tank 610may also include a pump (not shown) for pumping the flowback fluid 620out of the tank 610.

In some embodiments, the flowback fluid 620 may be treated by addingcarbon nitride to the tank 610. The carbon nitride may be mixed into theflowback fluid 620 with mixer 630 to cause the carbon nitride toadequately contact the flowback fluid 620. The carbon nitride maycapture (i.e., scavenge) contaminants of the flowback fluid 620 in thetank 610. The pH of the flowback fluid 620 may be controlled within arange between about 6.0 and about 8.0 to optimize removal of thecontaminants.

The system 600 may include a carbon nitride material 660 within theinlet piping to the tank 610 and another carbon nitride material 665within the outlet piping of the tank 610. The carbon nitride material660, 665 may be similar to the carbon nitride as described above withreference to 560 in FIG. 5. Thus, the flowback fluid 620 may be treatedas it enters and/or exits the tank 610 in addition to being treatedwithin the tank 610.

EXAMPLE

A mixture was prepared by spiking a water sample with a standardsolution of heavy metals. The solution included heavy metal cations andother ions, including boron, barium, chromium, copper, iron, potassium,magnesium, manganese, molybdenum, sodium, nickel, lead, sulfate,silicon, titanium, and zinc. The solution was prepared with an originalpH of about 1.7.

A second solution was prepared from the first solution by treating thefirst solution with 50% NaOH to increase the pH to approximately 6.98.Each of the first and second solution were filtered through a 25 μmfilter. Then, each of the first and second solutions was treated withapproximately 1 gram of carbon nitride nanoparticles. A significantdecrease in the concentration of particular cations was observed aftertreating the solutions with the carbon nitride nanoparticles. Theresults are shown in Table 1 below.

TABLE 1 Carbon nitride treatment at pH of 1.7 and pH of 6.98 pH = 1.7 pH= 1.7 pH = 1.7 pH = 6.98 pH = 6.98 pH = 6.98 Pre-treatment ConcentrationPercent Pre-treatment Concentration Percent concentration after treatingreduction by concentration after treating reduction by Ion (ppm) (ppm)treatment (ppm) (ppm) treatment B 12.09 11.76 3 12.08 11.56 8 Ba 4.193.90 7 4.10 3.67 13 Cr 3.89 2.28 41 2.34 0.44 89 Cu 3.50 1.18 66 2.110.34 90 Fe 10.00 4.03 60 8.97 0.47 97 K 1300 1270 2 1317 1278 5 Mg 14711457 1 1449 1417 6 Mn 2.56 2.42 5 2.12 1.40 48 Mo 3.00 1.52 49 3.23 2.3937 Na 64470 63720 1 65540 63580 6 Ni 4.07 3.33 18 3.34 1.50 64 Pb 3.512.63 25 2.11 0.46 87 SO₄ 175 174 1 179 174 5 Si 6.73 5.30 21 4.80 3.3450 Ti 4.49 2.36 47 2.79 0.54 89 Zn 7.88 5.82 26 5.20 1.20 85

Thus, the carbon nitride was effective at removing cations from asolution containing heavy metal cations. The carbon nitride moreeffectively removed cations from a solution having a neutral pH(pH=6.98), than from a solution having an acidic pH (pH=1.7).

While the disclosure is susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, the disclosure is not intended to be limited to the particularforms disclosed. Rather, the disclosure is to cover all modifications,equivalents, and alternatives falling within the scope of the disclosureas defined by the following appended claims and their legal equivalents.

1. A method of forming a material for removing contaminants from afluid, the method comprising: providing a carbon nitride material havinga structure comprising vacancies between triazine rings of the carbonnitride material; mixing the carbon nitride material with at least oneof an elastomeric material, polyurethane, polyurea, polyamine, carbonblack, graphite, carbon fiber, glass fiber, silica, a clay, calciumcarbonate, bentonite, polytetrafluoroethylene, and molybdenum disulfide;and forming at least one of a filter or a membrane comprising the carbonnitride material, wherein the at least one of a filter or a membranecomprises between about fifteen percent by weight and about thirty-fivepercent by weight of the carbon nitride material.
 2. The method of claim1, further comprising disposing the carbon nitride material within ahousing configured to contain the carbon nitride material.
 3. The methodof claim 1, further comprising selecting the elastomeric material tocomprise one or more of acrylonitrile butadiene styrene,polyacrylonitrile, a nitrile-based elastomer, or combinations thereof.4. The method of claim 1, further comprising selecting the carbonnitride material to comprise a C₃N₄ polymer material.
 5. The method ofclaim 1, further comprising selecting the carbon nitride material tocomprise graphitic carbon nitride.
 6. The method of claim 1, furthercomprising selecting the carbon nitride material to comprise particleshaving an average particle diameter between about 100 nm and about 1,000nm.
 7. The method of claim 1, further comprising functionalizing thecarbon nitride material with hydrophobic groups.
 8. The method of claim1, further comprising functionalizing the carbon nitride material withalkyl groups, vinyl groups, epoxide groups, silane groups, carboxylgroups, pyridine groups, phenolic groups, or combinations thereof.
 9. Anarticle for removing contaminants from a fluid, the article comprising:at least one of a nitrile-based elastomer, acrylonitrile butadienestyrene, polyacrylonitrile, polyurethane, polyurea, a polyamine, orcombinations thereof; and between about 5 weight percent and about 100weight percent carbon nitride, the carbon nitride comprising a pluralityof triazine rings.
 10. The article of claim 9, further comprising atleast one absorbent material.
 11. The article of claim 9, furthercomprising a cellulose material.
 12. The article of claim 9, furthercomprising at least one of carbon black, graphite, carbon fiber, glassfiber, silica, a clay, calcium carbonate, bentonite,polytetrafluoroethylene, and molybdenum disulfide.
 13. The article ofclaim 9, wherein the article comprises at least a portion of a membrane,a filter, or a swellable material.
 14. The article of claim 9, whereinthe article comprises between about 15 weight percent and about 35weight percent carbon nitride.
 15. The article of claim 9, wherein thearticle comprises between about 35 weight percent and about 50 weightpercent carbon nitride.
 16. The article of claim 9, wherein the carbonnitride is functionalized with alkyl groups, vinyl groups, epoxidegroups, silane groups, carboxyl groups, pyridine groups, phenolicgroups, or combinations thereof.
 17. The article of claim 9, wherein thecarbon nitride comprises a C₃N₄ polymer material.
 18. The article ofclaim 9, further comprising an acrylic resin binder, an acrylic polymer,or a combination thereof.
 19. A method of forming a material forremoving contaminants from a fluid, the method comprising: mixing carbonnitride with at least one of a nitrile-based elastomer, acrylonitrilebutadiene styrene, polyacrylonitrile, polyurethane, polyurea, apolyamine, or combinations thereof to form a carbon nitride materialcomprising between about 5 weight percent and about 100 weight percentcarbon nitride; and forming at least one of a filter, a membrane, or aswellable material comprising the carbon nitride material.
 20. Themethod of claim 19, further comprising reacting terminal amino groups ofthe carbon nitride with polyurethane, polyurea, a polyamine, orcombinations thereof.